1. Field of the Invention
The present invention relates to a sheet stacking system, a method of controlling the same, and a storage medium.
2. Description of the Related Art
In a system including a printing apparatus and a post processing apparatus for executing post processing for sheets printed by the printing apparatus, it is important to efficiently and accurately process a large volume of materials printed by the printing apparatus. In particular, a situation in which the printing speed of the printing apparatus drops under the influence of the operation of the post processing apparatus should be avoided. A work process should be designed to prevent generation of a work error in processing a printed material by an operator.
Japanese Patent Laid-Open No. 2009-269303 discloses a technique in which, when an instruction is input during print processing by a printing apparatus to take out printed sheets stored in a large-volume stacker serving as an example of a post processing apparatus, the discharge destination of sheets to be discharged from the printing apparatus is changed to another place. Even when taking out printed sheets from the stacker, the print operation can continue without interrupting the print processing by the printing apparatus.
A large-volume stacker includes a lift table which receives and stacks printed sheets discharged from the printing apparatus and can move up and down depending on the state of the stacked sheet bundle. To eject a sheet bundle stacked on the lift table from the stacker, some large-volume stackers are equipped with an ejection table which receives the sheet bundle from the lift table so that the user can take it out from the stacker. When the lift table becomes full of sheets discharged from the printing apparatus or sheets are stacked to a predetermined height on the lift table, the large-volume stacker reloads the sheet bundle on the lift table to the ejection table so that the sheet bundle can be taken out from the stacker. The large-volume stacker returns the blank lift table to the original position where the lift table can receive and stack sheets discharged from the printing apparatus. The large-volume stacker then continues the operation of stacking sheets discharged from the printing apparatus on the lift table. However, a time of several tens of seconds is taken to reload a sheet bundle from the lift table to the ejection table. Meanwhile, the large-volume stacker cannot receive sheets discharged from the printing apparatus. Thus, the printing apparatus temporarily interrupts the print operation, decreasing the productivity.
To prevent the decrease in productivity caused by interruption of print processing by the printing apparatus when printed sheets are taken out from the stacker, a plurality of large-volume stackers may be connected to the printing apparatus. In this case, while the first large-volume stacker executes the operation of reloading a sheet bundle to the ejection table when the lift table becomes full, subsequent printed sheets discharged from the printing apparatus are stacked on the lift table of the second large-volume stacker. By performing this operation, the printing apparatus can continuously execute the print operation, preventing generation of the above-described situation in which the productivity decreases. This operation is advantageous in terms of the productivity.
It is also important to prevent generation of a work error as much as possible when the operator processes printed sheets. The sheet process by the operator is, for example, work of carrying a sheet bundle stacked on the large-volume stacker to the next post processing apparatus. When a plurality of large-volume stackers are used, the operator needs to do work by always being aware of a large-volume stacker to which target printed sheets are discharged. When the lift table of one stacker becomes full and the discharge destination of printed sheets is automatically switched to another stacker, as described above, it becomes difficult for the operator to grasp the order of sheets.
As described above, there are two challenges to perform the print operation for a large volume of sheets without decreasing the productivity and to clarify work by an operator who processes a large volume of printed sheets.